It is conventional to set a well lock in a landing nipple in a tubing string in a well such as the series DB of Camco, Incorporated as disclosed in the General Catalog of 1975-76 Equipment and Services of Camco, Incorporated for supporting various well equipment. The landing nipple includes a locking notch for receiving locking dogs from the well lock and includes a landing shoulder which protrudes into the landing nipple bore for contacting a no-go shoulder on the lock for locating the lock and allowing a downward force to be applied to the lock for actuating the locking dogs outwardly into the locking notch. However, after the lock is set, any high downward force in the well bore on the lock creates an enormous force per unit area between the no-go shoulder and the landing shoulder of the nipple because of the small contact area. This creates the possibility that the landing shoulder of the nipple may be deformed and may create burrs which may tear up and damage the sealing packing of subsequent locks and well equipment and/or may deform the no-go shoulder of the nipple and the lock housing. U.S. Pat. No. 4,457,368 discloses an improved no-go shoulder by providing a shearable no-go plastic shoulder insert. However, such a plastic insert may prematurely fail. Furthermore, problems may arise in a conventional lock in that well fluids may flow outwardly through the well lock and erode and damage the nipple interior. Additionally, prior art well locks generally use a setting collet which can be engaged and deformed by upwardly moving well tools through the lock.
The present invention is directed to a well lock having retractable no-go dogs which, when the lock is set, may retract instead of deforming the nipple landing shoulder or the dogs. The present invention may also avoid the use of collets on the lock expander for reducing deformation of the expander tube in use, and may utilize a seal to prevent the flow of well fluid from eroding the well nipple.